Doppler tracking processor and time of closest approach detector

Abstract

Disclosed is a Doppler tracking processor and time of closest approach detector for use in active or semi-active radar-guided missiles. A known processor uses a fractional Doppler gate (FDG) to process the Doppler signal to activate the warhead detonation properly at time of closest approach (TCA); it indicates when the Doppler energy has rolled off to, for example, one-half the pre-intercept Doppler frequency. The present invention uses a Doppler tracking processor and TCA detector. The tracking filter can extract the instantaneous value of the Doppler frequency even during roll-off. The system processes the Doppler from the pre-intercept frequency up to an appropriate fractional frequency occurring at TCA, at which time it provides a signal for use in warhead detonation.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A Doppler tracking processor and time of closest approach detector system comprising: first means for deriving a reference signal proportional to a predetermined fraction of the frequency of a Doppler signal, said first means comprising a fractional ratio converter having an input to receive a voltage proportional to the Doppler signal, said converter having filtering and attenuation means for deriving said reference signal from said voltage;   second means for deriving a second signal which is dynamic and is proportional to the instantaneous Doppler frequency of the Doppler signal during Doppler roll-off; and   comparator means for comparing said second signal and said reference signal, said comparator producing an output signal if said second signal drops below said reference signal.   
     
     
       2. A system as claimed in claim 1 wherein said second means comprises a tunable band-pass filter having a first input to receive said Doppler signal, a control input, and an output, said output being connected to the input of a feedback loop having an output connected to the control input of the tunable band-pass filter. 
     
     
       3. A system as claimed in claim 2 wherein the output of the feedback loop is also connected to a low-pass filter, said low-pass filter having an output connected to said comparator. 
     
     
       4. A system as claimed in claim 3 wherein said feedback loop comprises a fast automatic gain control circuit followed by a fast frequency-to-voltage converter. 
     
     
       5. A system as claimed in claim 4 further including means for scaling said reference signal to the output of the frequency-to-voltage converter. 
     
     
       6. A system as claimed in claim 5 further including means for continuously tuning the tunable bandpass filter over the 5-140 kHz band. 
     
     
       7. A system as claimed in claim 6 wherein the feedback loop includes means for adjusting the center frequency of the tunable band-pass filter to keep its band-pass center frequency in substantial coincidence with the component of greatest amplitude in the Doppler signal.